A hinge device absorbing a drop impact of rotatable components such as a sound board of a piano and lid of a record player, lap top computer, copier, various office equipment or a stool was disclosed by a Japanese Utility Model Application Laid-open No. 62-81739.
As shown in FIG. 12, a hinge of the prior art comprises a case 41 to be fastened on a stationary component such as a stool, a rotatable component 42 to be connected to a lid thereof, a high viscosity grease filled in a gap between the case 41 and the rotatable component 42, and a coil spring 43 mounted between the bottom of the case 41 and the rotatable component 42.
However, in this conventional hinge device, the rotatable component 42 and a shaft 44 to be connected to a stool lid are integrally constructed. Therefore, the case 41 must be fastened to a stool after connecting the shaft 44 to the stool lid which causes poor assembly. Besides, it is impossible to manufacture the case 41 integrally with a stool.
Also, since a pair of "O" rings 45 and 46 are inserted into ring grooves, the rotatable component 42 must have enough thickness for forming the ring grooves therein, thus causing an increase in weight. In addition, it is hard to insert the rotatable component 42 into the case 41 due to the frictional force of the "O" ring 46 which has to slide on the whole inner wall of the case 41. Also, it is easy to apply grease on only an outer surface of the rotatable component 42, but it is almost impossible to do the same on the inner wall of the case 41.
The present invention was developed taking the above problems into consideration and provides a light hinge device enabling an easy assembling operation.